1. Field of the Invention
The present invention relates to color ink jet recording method/apparatus for forming color images on a recording medium by use of ink of plural colors.
2. Related Background Art
There has been known conventionally a color ink jet recording method for forming color images by discharging ink of plural colors from discharge ports for the adhesion thereof to a recording medium. A color ink jet recording method of the kind forms in general color images in mixed colors using four colors of ink, yellow (Y), magenta (M), cyan (C), and black (K). Then, for the formation of secondary color, such as R (red), G (green), and B (blue), the aforesaid three colors, yellow (Y), magenta (M), and cyan (C), are appropriately combined and mixed.
This color ink jet recording method is an excellent recording method which makes it possible to implement recording in high image quality at high speed with less noise, and at lower cost. In recent years, therefore, the color ink jet recording method has been widely utilized for a printer, a copying machine, a facsimile machine, and much other office equipment. Further, this method is used for a large-size plotter, and even utilized for printing color proofs, posters, and others in the printing industry.
Now that the ink jet recording technologies are applied not only to office equipment, but also to other equipment such as used in the industrial fields, it is desired to provide color images in much higher quality with higher durability. For a method for forming images in higher quality, various proposals have been made with various points of view. For example, there is a method of increasing the number of gradations that can be represented by use of darker and lighter ink, a method of reducing the granular senses of dots by attempting to make small liquid droplets finer still, or the like.
Conventionally, however, only the execution of the aforesaid method is not good enough to record images in higher quality. In order to attain recording in higher quality with a different angle of view, there are encountered problems yet to be solved as given below.
Firstly, there is a problem related to the saturation of images. As described above, when recording should be made in secondary colors by the ink jet method, ink containing colorant of different colors should be superposed to mix colors for obtaining a desired resolution in some cases. When ink of different colors should be mixed as described above, the ink colorant on the lower layer is subjected to being influenced by the ink colorant on the upper layer with resultant light scattering, thus making it difficult to obtain stable color reproduction. Also, the saturation of ink dots is reduced inevitably due to the two to three ink dots which are superposed on the same landing point. With such reduced saturation, the range of color reproduction is made narrower eventually. In contrast, if saturation is made higher, the range of color reproduction is widened to make it possible to obtain images in higher quality. Therefore, it is desired to provide a recording method in which saturation may be made higher. Also, in order to improve an image representation, there is a method of enhancing the density of ink, that is, a method of making the density of the colorant in ink higher. But, if droplets of the ink whose colorant is made denser are superposed on the same landing point one after another, saturation becomes lower still and the range of color reproduction is made narrower accordingly. As for a printed object for outdoor use, such as a poster, pigments are generally used as colorants in order to strengthen the light resistance. As a result, if pigments are used in the ink jet method, the reduction of saturation as described above becomes more conspicuous.
Secondly, there is a problem related to the change of color tones (or color flavors) depending on the order in which ink of different colors is superposed. Here, bidirectional printing is effective for high speed recording, but the bidirectional printing brings about the different order of ink superposition eventually. Then, in some cases, the color tones are caused to change due to the different order of ink superposition. The lesser the change of color tones, the higher becomes the quality of image recorded. Thus, for recording images in high quality at high speed, it is desired to provide a recording method which Is capable of reproducing colors irrespective of the order in which ink of different colors should be superposed.
Thirdly, at the end, there is a problem related to blurring due to ink superposition. When recording in secondary colors, ink of different colors is superposed on the same landing point. As a result, the amount of ink to be shot onto a recording medium becomes greater than that of ink to be shot for monochromatic recording. Thus, depending on the ink absorption capability of a recording medium to be used, ink is not absorbed good enough and may blur eventually in some cases. Also, in order to prevent the blurring, it is possible to make an arrangement so as to shoot the second ink droplet onto a recording medium at a sufficient interval after the shooting of the first one. However, this requires a longer period for recording. Ink blurring should preferably be reduced without making the recording period longer.
Under such circumstances, the inventors hereof have found it necessary to solve the problems related to the reduction of saturation, the difference in color tones, the blurring of ink, and the reduction of throughput simultaneously when recording in secondary colors, and have designed the present invention after various attempts with a view to solving them at the same time.
Here, therefore, with a view to solving the first to third problems discussed above, the present invention is designed. It is an object of the invention to provide color ink jet recording method/apparatus capable of reducing blurring of ink dots without reducing dot saturation, generating no difference in tones of secondary colors, and inviting no reduction of throughput.
In order to achieve these objects, there is provided a color ink jet recording method of the invention, which forms a color image on a recording medium by discharging ink of plural colors from an ink jet head in accordance with image data to enable monochrome dot(s) to apply to one pixel, featured by comprising the step of performing a recording operation in accordance with all the data of the image data by forming on the recording medium ink dots of plural colors having the optical density of 1 or more and 1.5 or less with an average dot diameter xcfx86(xcexcm) after fixation of ink applied thereon being (2.54xc3x97104/R)xe2x89xa6xcfx86xe2x89xa6({square root over (2)}xc3x972.54xc3x97104/R) (where R is resolution in units of dpi (dot/inch)).
Also, there is provided the color ink jet recording apparatus of the invention, which forms a color image on the recording medium in accordance with image data by discharging ink to a recording medium to enable monochrome dot(s) to apply to one pixel scanning an ink jet head having a plurality of discharge ports for discharging ink of plural colors, relatively to the recording medium, featured by comprising driving means for causing the ink jet heads to record in accordance with the image data so as to enable ink dots of plural colors having the optical density of 1 or more and 1.5 or less to be within a range of an average dot diameter xcfx86(xcexcm) after fixation of ink applied thereon being (2.54xc3x97104/R)xe2x89xa6xcfx86xe2x89xa6({square root over (2)}xc3x972.54xc3x97104/R) (where R is resolution, unit being dpi (dot/inch)).
Here, also, is provided by the present invention a method for processing image data to form a color image on a recording medium by discharging ink of plural colors from an ink jet head in accordance with image data, featured by comprising the steps of providing image data on an image to be formed; and processing the image data for recording in accordance with all the data of the image data by forming on the recording medium, by enabling monochrome dot(s) to apply to one pixel, ink dots of plural colors having the optical density of 1 or more and 1.5 or less with an average dot diameter xcfx86(xcexcm) after fixation of ink applied thereon being (2.54xc3x97104/R)xe2x89xa6xcfx86xe2x89xa6({square root over (2)}xc3x972.54xc3x97104/R) (where R is resolution, unit being dpi (dot/inch)).
Here, also, is provided by the present invention an apparatus for processing image data to form a color image on a recording medium by discharging ink of plural colors from an ink jet head in accordance with image data, featured by comprising means for processing image data to process the image data for recording in accordance with all the data of the image data by forming on the recording medium, by enabling monochrome dot(s) to apply to one pixel, ink dots of plural colors having the optical density of 1 or more and 1.5 or less with an average dot diameter xcfx86(xcexcm) after fixation of ink applied thereon being (2.54xc3x97104/R)xe2x89xa6xcfx86xe2x89xa6({square root over (2)}xc3x972.54xc3x97104/R) (where R is resolution, unit being dpi (dot/inch)).
In addition, it is noted that one inch referred to in the specification hereof means 2.54 cm.
Also, in the specification hereof, the phrase xe2x80x9ceach of ink dots is not essentially superposedxe2x80x9d is assumed to include a degree of dot superposition to the extent that given the radius of an ink dot as r, the distance 1 between centers of adjacent dots satisfies the relation of {square root over (2)}rxe2x89xa61xe2x89xa62r. In other words, the degree of dot superposition shown in FIG. 6 is minimum, and the one shown in FIG. 7 is maximum.